The present invention relates generally to the field of circuit breakers and more particularly to a molded case circuit breaker with a shunt trip device.
In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are two modes by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as 160 amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range.
In the event of current levels above the normal operating level of the thermal overload release, it is desirable to trip the breaker without any intentional delay, as in the case of a short circuit in the protected circuit, therefore, an electromagnetic trip element is generally used. In a short circuit condition, the higher amount of current flowing through the circuit breaker activates a magnetic release which trips the breaker in a much faster time than occurs with the bi-metal heating. It is desirable to tune the magnetic trip elements so that the magnetic trip unit trips at lower short circuit currents at a lower continuous current rating and trips at a higher short circuit current at a higher continuous current rating. This matches the current tripping performance of the breaker with the typical equipment present downstream of the breaker on the load side of the circuit breaker.
In certain situations, an operator of an electrical system may desire to open a circuit breaker from a remote location. Such circumstances can include applications for maintenance and control. It may also be used in applications to provide synchronizing of several breakers, together with other accessories, to open and close several circuit breakers. One device used for tripping a circuit breaker from a remote location is a shunt trip accessory. The shunt trip accessory currently used have several disadvantages. Some such shunt trip accessories must be installed in the circuit breaker housing behind the main cover and in close proximity to electrically live parts and connections. Other shunt trip accessories require the user to provide terminal connections to the shunt trip wires. Further examples of present shunt trip accessories are designed to be used with a single circuit breaker frame, i.e., for each current rating of the circuit breaker a specially designed shunt trip accessory is required.
Thus, there is a need for a shunt trip accessory to open a circuit breaker from a remote location that can be installed in the main cover of the circuit breaker without exposing the electrically live arts of the circuit breaker. There is a further need for a shunt trip device that can be used with several circuit breaker frame sizes, that is a single shunt trip device that will operate over a wide range of current ratings for the circuit breaker. There is an additional need for a shunt trip device with which a customer can connect its control wiring directly to the shunt trip device without any additional rewiring. And further, there is a need for a shunt trip device for a circuit breaker that can be installed in a circuit breaker utilizing a common latching protrusion that provides an audible snap fit installation.
The present invention provides a shunt trip device for a molded case circuit breaker with the circuit breaking having an operating mechanism, a trip bar and a cover. The shunt trip device comprises a base and a top mount with a solenoid having a plunger mounted on the base. The shunt trip bar actuator is attached to a push plate member mounted on the base and aligned with the plunger of the solenoid. The shunt trip bar actuator is aligned and in selective contact with the trip bar of the circuit breaker. A spring installed between the solenoid and the push plate member biases the push plate and trip bar actuator assembly towards a reset position. A clearing switch is mounted on the base and connected in series with the solenoid. The clearing switch is coupled to a cross bar switch actuator which is in contact with the operating mechanism of the circuit breaker. Upon receiving a control power signal from a remote location, the solenoid is energized and the plunger forces the shunt trip device against the trip bar of the circuit breaker thereby unlatching the operating mechanism of the circuit breaker and opening the contacts in the circuit breaker housing. When the circuit breaker operating mechanism opens, the cross bar in the operating mechanism moves the cross bar switch actuator in the clearing switch thereby opening the clearing switch and cutting off power to the solenoid. The spring then forces the push plate member back into its reset position. The clearing switch cannot be reset until the circuit breaker is closed and the cross bar of the circuit breaker moves the cross bar switch actuator back to its reset position.
The circuit breaker of the present invention includes a molded housing including a main breaker cover, a first terminal and a second terminal mounted in the casing with a contact electrically coupled to the first terminal and a movable contact electrically coupled to the second terminal. It also included an operating mechanism having a pivoting member movable between an ON position, an OFF position and a TRIPPED position, wherein the pivoting member is coupled to the movable contact. An intermediate latching mechanism mounted in the housing and coupled to the operating mechanism is in selective operative contact with a trip unit having a trip bar. The trip unit is also coupled to the movable contact and the second terminal. An accessory socket formed in the main breaker cover, on either side of an opening for the pivoting member is in communication with the housing. A latching protrusion mounted in the socket engages an accessory installed in the accessory socket. An accessory cover sized to cover the accessory mounted in the accessory socket is also provided. One such accessory that can be installed in the socket is a shunt trip device which will trip the circuit breaker upon receiving a power signal from a remote location.
The present invention also includes a method for tripping a molded case circuit breaker having an operating mechanism configured to open and close a power circuit, a trip unit with an intermediate latch and a breaker cover with the tripping of the circuit breaker occurring from a remote location. The method for tripping comprising the steps of closing the circuit breaker with the operating mechanism, installing a shunt trip device in the circuit breaker cover, providing power to the solenoid through a clearing switch from a remote location whereby the solenoid forces the trip unit to unlatch the operating mechanism to open the power circuit and then moving the clearing switch to an open position with the operating mechanism whereby power to the solenoid is cut off.